Surveillance imaging systems traditionally use off-the-shelf general-purpose imagers for video acquisition. A luminance channel in the imager provides a luminance signal having a dynamic range that is large enough to convey a scene to a viewer. The luminance channel is normally limited by an automatic iris lens setting. A scene comprising dark foreground and a bright background is both common and problematic. In such a scene, the detail in the foreground is often limited to a few brightness or intensity levels near the bottom of the luminance channel dynamic range, while the objects in the background are crowded into a few levels near the top. When viewed on a monitor, little information can be extracted from this scene. Automatic luminance channel gain circuits may be used to improve the contrast in the brightest portions of the scene, though usually at the expense of the darker portions.
Therefore, a need exists in the art for a method and apparatus for performing improved contrast enhancement.